ABSTRACT: Vibrio parahaemolyticus is a marine bacterium that causes human gastroenteritis. Most clinical
isolates produce a major virulence factor known as the thermostable direct hemolysin (TDH).
However have been isolated V. parahaemolyticus strains lacking tdh genes from patients with
gastroenteritis. Besides this, exist evidence that support that TDH is not exclusive of Vibrio
parahaemolytcus and is present in different Vibrio species, probably by lateral transfer. Recently, it
has been demonstrated that TDH encoded by the tdh gene, in a clinical strain, was partially deleted
by the transposition of the insertion sequence, ISVpa3. In order to add to understand the changes to
the characteristics of V. parahaemolyticus occur during infection, we examined the surrounding tdhA
gene, of the sequence strain RIMD2210633, for the presence of more insertion sequences. Was
founded two 849‐bp IS flanking the tdhA gene forming a structure like a composite transposon. The
presence of the transposase was detected by Westtern blott. The functionality of the transposón was
demonstrated by the generation of auxotophic mutants as consequences of the interference of
metabolic genes by the transposón. Therefore the evidences suggest the presence of a functional
transposase that can be responsible of the transpose action of the composite transposon and the
generation of strain lacking tdhA gene.